For treating patients with certain diseases use is made of concentrates of blood components which are administered to the patients. The blood component concentrates may be obtained by subjecting whole blood to density centrifuging. They should exhibit the lowest possible concentration of leukocytes because they may trigger immune reactions in the patient. For this reason an attempt is made to remove leukocytes from blood preparations.
Filters for separating leukocytes from blood preparations are known in the art. For example, the patents U.S. Pat. No. 4,880,548, U.S. Pat. No. 5,445,736 and U.S. Pat. No. 5,580,465 describe filters which are able to separate leukocytes (WBC) from concentrates of blood platelets (PLT). However, such filters are not suitable for separating leukocytes from whole blood because the erythrocytes (RC) are modified on contact with the filter material.
The separation of leukocytes from whole blood is described in U.S. Pat. No. 5,895,575. The filter material incorporates a hydrophobic support material, for example a fibre non-woven fabric of polyethylene terephthalate, to which a hydrophilic polysaccharide soluble in water is applied. The problem here is the relatively low separation of the leukocytes from whole blood. Compared to the filters described in U.S. Pat. No. 4,880,548, the filters coated with the polysaccharides separate far fewer leukocytes from the blood preparation. Although this separation can be improved by means of nitrocellulose filters, such systems are expensive to purchase and use. Moreover, the water solubility of the coating material is a problem. Since whole blood contains large quantities of water, the coating material may be washed out. As a result of this, however, thrombocytes or platulocytes are retained on the filter material. The particular problem here is that this loss takes place continuously. Although a cross-linking reaction intended to reduce the solubility is described in U.S. Pat. No. 5,895,575, such cross-linking causes further problems. In particular, residues of the cross-linking agent may reach the blood circulation. Furthermore, very intense cross-linking may result in reduced permeability of the filter. Too little cross-linking, however, may not prevent wash-out completely.